1. Field of the Invention
The present invention relates to a hybrid vehicle equipped with an internal combustion engine, a generator, and a motor.
2. Description of the Related Art
Hitherto, as this type of hybrid vehicle, there has been known a hybrid vehicle equipped with an internal combustion engine, a generator connected to a drive shaft of the internal combustion engine, a motor, and an output shaft which is connected to the drive shaft of the motor and which also permits connection to the drive shaft of the internal combustion engine through the intermediary of an engaging/disengaging device, wheels being connected to the output shaft, as disclosed in the publication of Japanese Patent No. 3183062 (hereinafter referred to as patent document 1).
The hybrid vehicle is capable of traveling in a travel mode which uses the driving force of the motor by engagement/disengagement performed by the engaging/disengaging device according to a traveling state of the vehicle, and also capable of traveling in a travel mode which uses the driving force of one or both of the motor and the internal combustion engine.
Here, as a motor that may be used as the motor for this type of hybrid vehicle, there is a motor disclosed in the publication of Japanese Patent Application Laid-Open No. 2004-72978 (hereinafter referred to as patent document 2). The motor has an inner rotor and outer rotor, which are coaxially disposed and which are respectively equipped with permanent magnets. The two rotors are set such that one rotor is allowed to relatively rotate within a certain angle range in relation to the other rotor, the relative rotation permitting the phase difference between the two rotors to be changed.
The motor uses a device for hydraulically generating a driving force for implementing the relative rotation between the two rotors, as disclosed in patent document 2. The device has a plurality of pairs of advance oil chamber and retard oil chamber formed inside the inner rotor by a member supporting the inner rotor and a member supporting the outer rotor. Hydraulic oil is supplied to one of the advance oil chamber and the retard oil chamber of each pair, while the hydraulic oil is drained from the other oil chamber thereby to generate the driving force for implementing the relative rotation between the inner rotor and the outer rotor by a pressure difference between the oil chambers.
In the motor having the inner rotor and the outer rotor respectively equipped with permanent magnets, the phase difference between the two rotors tends to balance at a predetermined phase difference by magnetic forces acting between the permanent magnets of the inner rotor and the permanent magnets of the outer rotor in a state wherein no driving force for implementing the relative rotation between the two rotors or no driving force for holding the phase difference between the two rotors at a certain target phase difference is being imparted between the two rotors from an outer source, i.e., in a state wherein the relative rotation of one rotor with respect to the other rotor can be freely carried out within a mechanically defined angle range. There is a case where the predetermined phase difference becomes a phase difference which causes the intensity of the resultant magnetic flux of the permanent magnets of the two rotors to be lower than a maximum intensity. For example, in a motor having the permanent magnets of the two rotors arranged as illustrated in FIG. 1 or FIG. 7 or FIG. 8 of the aforesaid patent document 1, the phase difference between the two rotors will be balanced at a phase difference which approximately minimizes the intensity of a resultant magnetic flux outside the outer rotor.
If the motor disclosed in patent document 2 is applied to the hybrid vehicle in patent document 1, then an electrically-operated hydraulic pump is preferably used as the source of supplying hydraulic oil to the motor in order to generate the driving force for carrying out the relative rotation between the two rotors even when the internal combustion engine stops. Further preferably, the hydraulic pump for supplying the hydraulic oil to the motor serves also as an engaging/disengaging device to implement engagement/disengagement.
However, if a malfunction of the hydraulic pump serving as the supply source of hydraulic oil occurs, then it becomes difficult to change the phase difference between the two rotors in the motor. In this case, if the motor is constructed to balance the phase difference between the two rotors at a phase difference which approximately minimizes the intensity of the resultant magnetic flux of the permanent magnets of the two rotors due to the interaction of the permanent magnets between the two rotors, then a torque that can be output by the motor will reduce. This makes it difficult for the driving force of the motor to satisfy required driving force for driving the vehicle. Further, a response failure or the like will occur in the engaging/disengaging operation of the engaging/disengaging means, possibly causing a transmission failure when the engaging/disengaging device is engaged to transmit the driving force of the internal combustion engine to wheels.